Vacuum-insulated glass windows with glass-bump spacers

ABSTRACT

Vacuum-insulated glass (VIG) windows ( 10 ) that employ glass-bump spacers ( 50 ) and two or more glass panes ( 20 ) are disclosed. The glass-bump spacers are formed in the surface ( 24 ) of one of the glass panes ( 20 ) and consist of the glass material from the body portion ( 23 ) of the glass pane. Thus, the glass-bump spacers are integrally formed in the glass pane, as opposed to being discrete spacer elements that need to be added and fixed to the glass pane. Methods of forming VIG windows are also disclosed. The methods include forming the glass-bump spacers by irradiating a glass pane with a focused beam ( 112 F) from a laser ( 110 ). Heating effects in the glass cause the glass to locally expand, thereby forming a glass-bump spacer. The process is repeated at different locations in the glass pane to form an array of glass-bump spacers. A second glass pane is brought into contact with the glass-bump spacers, and the edges ( 28 F,  28 B) sealed. The resulting sealed interior region ( 40 ) is then evacuated to a vacuum pressure of less than one atmosphere.

PRIORITY

This application is a divisional application of and claims priority toU.S. patent application Ser. No. 12/265,192, filed Nov. 5, 2008, nowU.S. Pat. No. 8,821,999, titled “Vacuum Insulated Glass Windows WithGlass Bump Spacers”.

FIELD OF THE INVENTION

The present invention relates generally to vacuum-insulated glasswindows, and in particular to such windows that employ glass-bumpspacers.

BACKGROUND ART

Vacuum-insulated glass (VIG) windows typically consist of two or moreglass panes with a vacuum in between, which provides improved thermaland noise insulating properties as compared to ordinary glass windows.To prevent sagging of the glass panes, discrete spacers are placedbetween the glass panes to prevent the panes from contacting each other.The spacers are typically made of aluminum, plastic, ceramic, or glassand are distinct from the glass panes, i.e., they are discrete elementsdisposed and fixed between the glass panes.

While present-day spacers are effective in separating the panes, theytend to be visible when looking through the window, thereby making thewindow unsightly. In addition, the need to dispose the discrete spacersbetween the panes and then fix the spacers to the panes adds cost andcomplexity to the VIG window manufacturing process.

SUMMARY

A first aspect of the present invention is a VIG window. The VIG windowincludes a first glass pane having a first body formed from a firstglass material and having first opposite surfaces and a first outeredge. The VIG window also includes a second glass pane spaced apart fromand disposed substantially parallel to the first glass pane at a firstdistance and having a second body formed from a second glass materialand having second opposite surfaces and a second outer edge. A firstedge seal is formed around the respective first and second outer edgesso as to define a first sealed interior region between the first andsecond glass panes, wherein the first sealed interior region has avacuum pressure of less than one atmosphere. The VIG window furtherincludes a first plurality of glass-bump spacers integrally formed withthe first glass pane in one of the first surfaces and consisting of thefirst glass material from the first body portion, and contacting thesecond glass pane so as to maintain the spaced apart first distance.

Another aspect of the invention is a method of forming a VIG window. Themethod includes, in a first glass pane having a first body portion witha first surface and a first edge and comprising a first glass material,integrally forming in the first surface a first plurality of glass-bumpspacers consisting of the first glass material from the first bodyportion. The method also includes bringing a second glass pane having asecond body portion with a second surface and a second edge andcomprising a second glass material in contact with the first pluralityof glass-bump spacers so that the first and second glass panes arespaced apart by a first distance between the first and second surfaces.The method additionally includes sealing the first and second edges todefine an interior region between the first and second glass panes, andthen forming a vacuum pressure of less than one atmosphere in theinterior region.

Another aspect of the invention is a VIG window product formed by aprocess that includes providing a first glass pane having a first bodyportion with a first surface and a first edge and comprising a firstglass material, and forming in the first glass pane first surface aplurality of glass-bump spacers that consist of the first glass materialfrom the first body portion. The process also includes bringing a secondglass pane having a second body portion with a second surface and asecond edge and comprising a second glass material in contact with theglass-bump spacers so that the first and second glass panes are spacedapart by a first distance between the first and second surfaces. Theprocess further includes sealing the first and second edges to define aninterior region between the first and second glass panes. The processalso includes forming a vacuum pressure of less than one atmosphere inthe interior region.

Additional aspects, features and advantages of the invention are setforth in the detailed description that follows and, in part, will bereadily apparent to those skilled in the art from that description orrecognized by practicing the invention as described herein, includingthe detailed description that follows, the claims, as well as theappended drawings.

It is to be understood that both the foregoing general description andthe following detailed description present embodiments of the invention,and are intended to provide an overview or framework for understandingthe nature and character of the invention as it is claimed. Theaccompanying drawings are included to provide a further understanding ofthe invention and are incorporated in and constitute a part of thisspecification. The drawings illustrate various embodiments of theinvention and, together with the description, serve to explain theprinciples and operations of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front-on view of an example two-pane VIG window according tothe present invention;

FIG. 2 is a cross-sectional view of the VIG window of FIG. 1 as viewedin the direction CS-CS;

FIG. 3 is a close-up cross-sectional view of an example glass-bumpspacer;

FIG. 4A is a cross-sectional view similar to FIG. 2 and that illustratesan example embodiment of a three-pane VIG window having a middle glasspane with glass-bump spacers formed in both surfaces of the middle pane;

FIG. 4B is similar to FIG. 4A, except that the second set of glass-bumpspacers are formed in the back glass pane rather than the middle glasspane;

FIG. 5A and FIG. 5B illustrate typical transmission curves (transmission(%) vs. wavelength (nm)) in the UV and visible wavelength spectrums fortransparent alkaline earth aluminosilicate glasses (FIG. 5A) andtransparent soda-lime glasses (FIG. 5B);

FIG. 6 is a schematic diagram of an example laser-basedglass-bump-forming apparatus used to form glass-bump spacers in a glasspane in the process of forming a VIG window;

FIG. 7 is a schematic diagram of an example embodiment of a laser lightbeam as formed from light pulses from a pulsed laser;

FIG. 8 is a bar graph that plots the laser power P (W), the distanceD_(F), and the glass-bump-spacer height H for a soda-lime glass pane,based on experimental data;

FIG. 9 is a three-dimensional image of a glass-bump spacer formed in a3-mm soda-lime glass pane sample;

FIG. 10 is a line scan of the glass-bump spacer of FIG. 9, revealing asubstantially hemispherical profile;

FIG. 11 is a three-dimensional image of a glass-bump spacer similar tothat shown in FIG. 9, except that the glass-bump spacer has asubstantially flat top portion;

FIG. 12 is a schematic side view of an example glass pane having aninfrared-reflective coating; and

FIG. 13 is a close-up, cross-sectional view of an uncoated glass-bumpspacer formed in the glass pane of FIG. 12.

DETAILED DESCRIPTION

For purposes of description herein, the terms “front,” “back,” “middle,”and derivatives thereof are relative terms used to facilitate describingthe apparatus and methods of the invention. Accordingly, it is to beunderstood that the invention may assume various alternativeorientations and step sequences, except where expressly specified to thecontrary. It is also to be understood that the specific devices andprocesses illustrated in the attached drawings and described in thefollowing specification are embodiments of the inventive conceptsdefined in the appended claims. Hence, specific dimensions and otherphysical characteristics relating to the embodiments disclosed hereinare not to be considered as limiting, unless the claims expressly stateotherwise.

The term “photo-induced absorption” is broadly understood to mean alocal change of the absorption spectrum of a glass pane resulting fromlocally exposing (irradiating) the glass pane with optical radiation.Photo-induced absorption may involve a change in absorption at awavelength or a range of wavelengths, including, but not limited to,ultra-violet, near ultra-violet, visible, near-infrared, and/or infraredwavelengths. Examples of photo-induced absorption in a transparent glasspane include, for example and without limitation, color-centerformation, transient glass defect formation, and permanent glass defectformation.

The description of the glass-bump spacers being “formed in” a glass panemeans that the glass-bump spacers grow out of the body portion of theglass pane and are formed from the glass material making up the glasspane, so as to outwardly protrude in a convex manner from the otherwisesubstantially flat glass-pane surface.

As used herein, a window is an article comprising two or more glasspanes that are at least partially transparent to electromagnetic (EM)radiation, including EM radiation having ultra-violet, nearultra-violet, visible, near-infrared, and/or infrared wavelengths.

VIG Windows With Integrally Formed Glass-Bumps

FIG. 1 is a front-on view of an example embodiment of a two-pane VIGwindow 10 according to the present invention. FIG. 2 is across-sectional view of the example VIG window 10 of FIG. 1 as viewed inthe direction CS-CS. Cartesian coordinates are shown for the sake ofreference. VIG window 10 includes two glass panes 20, namely a frontglass pane 20F and a back glass pane 20B disposed opposite to andsubstantially parallel to one another. Front glass pane 20F has a bodyportion 23F made of a first glass material and has outer and innersurfaces 22F and 24F and an outer edge 28F. Likewise, back glass pane20B has a body portion 23B made of a second glass material and has outerand inner surfaces 22B and 24B and an outer edge 28B. In an exampleembodiment, the first and second glass materials making up body portions23F and 23B are the same.

Front and back glass panes 20F and 20B are separated by a distance D_(G)as measured from their respective inner surfaces 24F and 24B. An edgeseal 30 is provided at respective outer edges 28F and 28B to surround atleast a portion of each outer edge to provide a hermetic seal. Edge seal30 and front and back glass pane inner surfaces 24F and 24B define asealed interior region 40. Sealed interior region 40 is preferably atleast partially evacuated so that it has a vacuum pressure of less thanone atmosphere, which provides VIG window 10 with desirable thermal andacoustic insulation properties.

VIG window 10 further includes a plurality of glass-bump spacers 50integrally formed in inner surface 24B of back glass pane 20B. FIG. 3 isa close-up view of an example glass-bump spacer 50. Note that glass-bumpspacers 50 are integrally formed in back glass pane 20B and are notadded as separate or discrete elements to VIG window 10. Thus,glass-bumps 50 are formed from (and thus consist of) the same materialas back glass pane 20B, and in fact are extensions of body portion 23B.Example methods of forming glass-bumps 50 are discussed in detail below.

In an example embodiment, glass-bump spacers 50 are regularly spacedwith respect to one another. Because glass-bump spacers 50 areintegrally formed in body portion 23B, they are substantially invisiblewhen VIG window 10 is viewed at regular (i.e., substantially normallyincident) viewing angles. Consequently, glass-bumps 50 are shown inphantom in FIG. 1. Glass-bump 50 has a “tip” or “top portion” 51, asshown in FIG. 3. As discussed below, top portion 51 need not be roundedas is shown in FIG. 3. Glass-bump spacers 50 contact front pane innersurface 24F and serve to maintain the separation distance D_(G) betweenfront and back glass panes 20F and 20B.

In an example embodiment, glass panes 20F and 20B are formed from panesof soda-lime glass, which further in an example embodiment have athickness T_(G) between 2 mm and 3 mm. In an example embodiment,glass-bump spacers 50 formed in soda-lime glass have a height (“bumpheight”) H in the range from 75 μm to 170 μm, more preferably in therange from 100 μm to 170 μm, and even more preferably in the range from150 μm to 170 μm. In an example embodiment, glass panes 20F and 20B havesubstantially the same thickness T_(G) (see FIG. 6).

FIG. 4A is a cross-sectional view similar to FIG. 2 and illustrates anexample embodiment of a three-pane VIG window 10 that includes a middleglass pane 20M sandwiched between front pane 20F and back pane 20B.Middle glass pane 20M has a body portion 23M of a third glass materialand has a front side 22M, a back side 24M and an edge 28M. First andsecond sets of glass-bump spacers 50 are respectively formed in both thefront and back sides 22M and 24M of middle pane 20M and respectivelyserve to maintain distance D_(GA) between middle glass pane 20M andfront pane 20F, and distance D_(GB) between the middle pane and backpane 20B. In the example embodiment shown in FIG. 4A, a single edge seal30 serves to seal edges 28F, 28M and 28B. In another example embodiment,multiple edge seals 30 are used, where one edge seal serves to seal atleast respective portions of edges 28F and 28M, and the other edge sealserves to seal at least respective portions of edges 28M and 28B (seeFIG. 4B).

Edge seal 30 and glass pane surfaces 24F and 22M define a first sealedinterior region 40A, while edge seal 30 and glass pane surfaces 24M and24B define a second sealed interior region 40B. Sealed interior regions40A and 40B are preferably evacuated so that they each have a vacuumpressure of less than one atmosphere, which provides triple-pane VIGwindow 10 with desirable thermal insulation and acoustic properties, andin particular with about twice the insulation of a two-pane VIG window10 such as shown in FIG. 1 and FIG. 2.

FIG. 4B is similar to FIG. 4A, and illustrates an alternate exampleembodiment of three-pane VIG window 10, wherein the second set ofglass-bump spacers 50 are formed in inner surface 24B of back glass pane20B rather than in the middle glass pane 20M. FIG. 4B also illustratesan example embodiment where multiple edge seals 30 are used, asdescribed above.

In an example embodiment, middle glass pane 20M is formed from soda-limeglass, and further in an example embodiment has a thickness T_(G)between 2 mm and 3 mm. In an example embodiment, the front, middle andback glass pane body portions 23F, 23M and 23B are made of the sameglass material.

While soda-lime glass is the most common window glass, the VIG windowinvention disclosed herein can be applied to any type of glass in whichintegral glass-bump spacers 50 can be formed using the methods describedin detail below. For example, the VIG window invention disclosed hereinapplies to low-iron (“ultra-clear”) window glasses, as well as to theother glasses introduced and discussed below.

Glass-Bump Spacer Formation

Available transparent glasses used for window panes tend to have verylittle absorption at wavelengths where high-power lasers are available,such as the near-infrared (NIR) band between about 800 μm and 1600 μm,or in the ultraviolet (UV) band between about 340 nm and about 380 nm.For example, alkaline earth aluminosilicate glasses and sodiumaluminosilicate glasses (e.g., glass such as Eagle²⁰⁰⁰® glass, EagleXG™glass, 1317 glass, and Gorilla™ glass, all available from CorningIncorporated, Corning, N.Y.) typically have a transmission spectra asshown in FIG. 5A, and soda-lime glass typically has a transmissionspectra as shown in FIG. 5B. As evident from FIG. 5A and FIG. 5B, thetransmission of alkaline earth aluminosilicate and soda-lime glasses ismore than about 85% (including Fresnel losses due to reflection at theglass/air interface) at a wavelength of 355 nm, which is insufficientfor heating even small volumes of glass to temperatures close to aworking point (˜10⁵ Poise) unless lasers with several hundred watts ofavailable output power are used.

Unexpectedly, for certain transparent glass panes, including thoseformed from alkaline earth aluminosilicate glasses (e.g., LCD glassessuch as the aforementioned Eagle 2000™ glass and Eagle XG™ glass),soda-lime glasses and sodium aluminosilicate glasses (e.g., theaforementioned 1317 glass and Gorilla™ glass), it has been found thatabsorption at the laser wavelength can be raised to a sufficient levelby transmitting an intense UV laser beam through the transparent glasspane. In particular, a high repetition-rate, nanosecond-pulse-width UVlaser was found to be the most effective. Several seconds of exposurewith such a pulsed UV laser beam was found to result in photo-inducedabsorption in the otherwise relatively low-absorption transparent glass.This induced glass absorption significantly increases at the UVwavelength, making it possible to locally heat the glass pane to itsworking temperature (using the same laser or a separate laser) andenables the formation of glass-bump spacers 50. The UV-generatedabsorption fades over a short period of time (e.g., a few seconds) oncethe irradiation is terminated.

Other types of lasers, such as mid-infrared-wavelength lasers, can beused instead of a UV laser for most transparent glass materials. Anexample mid-infrared-wavelength laser generates a laser beam having awavelength of about 2.7 μm. A UV laser is described and considered belowin connection with the apparatus used to perform the methods of thepresent invention for the sake of illustration.

FIG. 6 is a schematic diagram of an example laser-based apparatus(“apparatus”) 100 used to form glass-bump spacers 50 in a glass pane 20in the process of forming VIG window 10. Apparatus 100 includes a laser110 arranged along an optical axis A1. Laser 110 emits a laser beam 112having power P along the optical axis. In an example embodiment, laser110 operates in the ultraviolet (UV) region of the electromagneticspectrum.

With reference also to FIG. 7, in a particular example embodiment, laser110 is a pulsed laser that generates light pulses 112P that constitutelaser beam 112, wherein the light pulses have a UV wavelength (e.g.,about 355 nm) and a nanosecond-scale temporal pulse width τ_(P). In anexample embodiment, light pulses 112P have a temporal pulse width τ_(P)in the range 20 ns≦τ_(P)≦80 ns, and a repetition rate R in the range 50kHz≦R≦200 kHz. Further in the example embodiment, laser 110 is a 20-Wattlaser (i.e., P=20 W). In an example embodiment, laser 110 comprises athird-harmonic Nd-based laser. As shown in FIG. 7, light pulses 112P arespaced apart in time by an amount Δt, thereby defining the repetitionrate as R=1/Δt.

Apparatus 110 also includes a focusing optical system 120 that isarranged along optical axis A1 and defines a focal plane P_(F) thatincludes a focal point FP. In an example embodiment, focusing opticalsystem 120 includes, along optical axis A1 in order from laser 110: acombination of a defocusing lens 124 and a first focusing lens 130(which combination forms a beam expander), and a second focusing lens132. In an example embodiment, defocusing lens 124 has a focal lengthf_(D)=−5 cm, first focusing lens 130 has a focal length f_(C1)=20 cm,and second focusing lens 132 has a focal length f_(C2)=3 cm and anumerical aperture NA_(C2)=0.3. In an example embodiment, defocusinglens 124 and first and second focusing lenses 130 and 132 are made offused silica and include anti-reflection (AR) coatings. Alternateexample embodiments of focusing optical system 120 include mirrors orcombinations of mirrors and lens elements configured to produce focusedlaser beam 112F from laser beam 112.

Apparatus 100 also includes a controller 150, such as a lasercontroller, a microcontroller, computer, microcomputer or the like,electrically connected to laser 110 and adapted to control the operationof the laser. In an example embodiment, a shutter 160 is provided in thepath of laser beam 112 and is electrically connected to controller 150so that the laser beam can be selectively blocked to turn the laser beam“ON” and “OFF” using a shutter control signal SS rather than turninglaser 110 “ON” and “OFF” with a laser control signal SL.

Prior to initiating the operation of apparatus 100, glass pane 20,having a body portion 23 with a front surface 22 and back surface 24, isdisposed relative to the apparatus. Specifically, glass pane 20 isdisposed along optical axis A1 so that front and back glass panesurfaces 22 and 24 are substantially perpendicular to the optical axisso that back glass pane surface 24 is slightly axially displaced fromfocal plane P_(F) in the direction towards laser 110 (i.e., in the +Zdirection) by a distance D_(F). In an example embodiment, glass pane 20has a thickness T_(G) in the range 1 mm≦T_(G)≦6 mm. Also in an exampleembodiment, 0.5 mm≦D_(F)≦2 mm. In this arrangement, glass-bump spacersare to be formed in glass pane surface 24, which corresponds to surface24B of back glass pane 20B of FIG. 2.

Laser 110 is then activated via control signal SL from controller 150 togenerate laser beam 112. If shutter 160 is used, then after laser 110 isactivated, the shutter is activated and placed in the “ON” position viashutter control signal SS from controller 150 so that the shutter passeslaser beam 112. Laser beam 112 is then received by focusing opticalsystem 120, and defocusing lens 124 therein causes the laser beam todiverge to form a defocused laser beam 112D. Defocused laser beam 112Dis then received by first focusing lens 130, which is arranged to forman expanded collimated laser beam 112C from the defocused laser beam.Collimated laser beam 112C is then received by second focusing lens 132,which forms a focused laser beam 112F. Focused laser beam 112F passesthrough glass pane 20 and forms a focus spot S along optical axis A1 atfocal point FP, which, as mentioned above, is at distance D_(F) fromglass pane back surface 24 and thus resides outside of body portion 24.It is noted here that glass pane 20 slightly affects the position offocal point FP of optical system 20 because focused laser beam 112Fconverges as it passes through the glass pane. However, the thicknessT_(G) of glass pane 20 is typically sufficiently thin so that thisfocus-shifting effect can be ignored.

A portion of focused laser beam 112F is absorbed as it passes throughglass pane 20 due to the aforementioned photo-induced absorption in theglass pane. This serves to locally heat glass pane 20. The amount ofphoto-induced absorption is relatively low, e.g., about 3% to about 4%.When focused light beam 112F is locally absorbed in glass pane 20, alimited expansion zone is created within body portion 23 in which therapid temperature change induces an expansion of the glass. Since theexpansion zone is constrained by unheated (and therefore unexpanded)regions of glass surrounding the expansion zone, the glass within theexpansion zone is compelled to relieve internal stresses by deformingupward, thereby forming a glass-bump spacer 50. As shown in the inset ofFIG. 6, glass-bump spacer 50 has a peak 51 corresponding to the locationof the highest beam intensity. In an example embodiment, glass-bumpspacer 50 is fixed by rapidly cooling the heated region of the glass. Inan example embodiment, this fixing is accomplished by terminating theexposure with (i.e., the irradiation by) focused laser beam 112F.

If focused light beam 112F has a circularly symmetric cross-sectionalintensity distribution, such as a Gaussian distribution, then the localheating and the attendant glass expansion occurs over a circular regionin glass pane body 23, and the resulting glass-bump spacer 50 issubstantially circularly symmetric.

In an example embodiment, a plurality of glass-bump spacers 50 areformed in glass pane 20 using the above method, and the glass pane isthen used to form VIG window 10. In an example embodiment, apparatus 100includes an X-Y-Z stage 170 electrically connected to controller 150 andconfigured to move glass pane 20 relative to focused laser beam 112F inthe X, Y and Z directions, as indicated by large arrows 172. This allowsfor a plurality of glass-bump spacers 50 to be formed by selectivelytranslating stage 170 via a stage control signal ST from controller 150and irradiating different locations in glass pane 20.

In an example embodiment, glass-bump spacers 50 are formed in a regulararray such as shown in FIG. 1. In an example embodiment, the spacingbetween adjacent glass-bump spacers 50 is between about 2 inches (i.e.,about 5.08 cm) and 6 inches (i.e., about 15.24 cm). Also in an exampleembodiment, glass-bump spacer formation is controlled using a feedbackdevice or system that tracks the growth of glass-bump spacers 50 so thatthe glass-bump spacers can be formed to have a select height H that issubstantially uniform over the set of glass-bump spacers.

In one example embodiment, glass-bump spacer formation is tracked bymeasuring the transmission T of focused laser beam 112F through glasspane 20. In an example embodiment, this is accomplished by arranging aphotodetector 180 along axis A1 at the output side of glass pane 20 andelectrically connecting the photodetector to controller 150. It turnsout that the transmission T of focused laser beam 112F rapidly decreaseswhen a glass-bump 50 is formed. Accordingly, this rapid drop intransmission is detected by a change in an electrical detector signal SDgenerated by photodetector 180 in response to detecting transmittedlight in focused laser beam 112F. Terminating the irradiation (exposure)with focused laser beam 112F (e.g., via the operation of controller 150using control signals SL or SS as described above) stops the localizedheating and fixes glass-bump spacer 50. In an example embodiment, themeasured transmission T is used to control the irradiation dose.

In an example embodiment, photodetector 180 is arranged adjacent theinput side of glass pane 20 and detects fluorescence from glass panebody 23 during the irradiation process. A threshold change in detectedfluorescence is then used to terminate the exposure or to adjust theirradiation dose.

In another example embodiment, a feedback sub-system can be used tocontrol the bump height of each glass-bump spacer by controlling theirradiating. For example, a feedback sub-system can be implemented tocontrol the irradiating by monitoring one or more of a transmissionintensity of the focused laser beam through the first glass pane, atemperature of each respective glass-bump spacer, a fluorescenceintensity emanating from each respective glass-bump spacer, and a bumpheight of each respective glass-bump spacer, and terminating theirradiating when a predetermined value of the monitored variable ismeasured.

In another example embodiment, focusing optical system 120 is adaptedfor scanning so that focused laser beam 112F can be selectively directedto locations in glass pane 20 where glass-bump spacers 50 are to beformed.

Bump height H depends in several factors, which include the laser powerP, the repetition rate R, the focusing conditions, and the glassmaterial making up glass pane 20. FIG. 8 is a bar graph that plots thelaser power (W) in focused laser beam 112F, distance D_(F) between focalplane P_(F) and back glass pane surface 24, and bump height H for aglass pane made of soda-lime glass having a thickness T_(G)=3 mm. Thebar graph of FIG. 8 is based in experimental data and provides anexample range of operating parameters for forming glass-bump spacers 50using apparatus 100 for the particular type of glass pane 20. Theexposure (irradiation) time used ranged between 2 s to 2.5 and it wasobserved that this variation did not significantly affect the bumpheight H. The optimum repetition rate of the UV laser was found to beR=150 kHz. The bump height H ranged from about 75 μm for D_(F) of about0.6 mm and a laser power P of about 9 W to about 170 μm for D_(F) ofabout 1.1 mm and a laser power of about 13 W.

Note that if bump heights H are too small, it could result in areduction in the amount of vacuum that can be applied to interior region40, leading to reduced insulation properties with too small a gapbetween adjacent glass panes 20. The smaller interior region volume thatresults also translates into reduced insulation properties. In addition,small bump heights H can give rise to the appearance of “Newton's rings”due to light interference between closely arranged glass surfaces. It isestimated that a bump height H≧100 μm is sufficient to overcome thesetwo potential problems for most VIG windows 10.

FIG. 9 is a three-dimensional image of a glass-bump spacer 50 formed ina soda-lime glass pane having a thickness T_(G)=3 mm. FIG. 10 is aline-scan of glass-bump spacer 50 of FIG. 9. The line scan reveals thatglass-bump spacer 50 has a substantially hemispherical shape, a bumpheight H of about 75 μm and a base diameter D_(B) of about 250 μm.

FIG. 11 is a three dimensional image of a glass-bump spacer 50 similarto that shown in FIG. 9, except that a growth-limiting surface in theform of a glass plate was placed adjacent glass pane surface 24 and thenthe glass pane irradiated as per above. The resulting glass-bump spacer50 grew to a certain bump height H and then this growth was limited bythe adjacent glass plate. The result was a glass-bump spacer 50 having asubstantially flat top portion 51 with a diameter D_(T). In this way,the size, height and shape of glass-bumps 50 can be controlled to somedegree, and in particular the diameter D_(T) (and thus the surface area)of substantially flat top portion 51 can be controlled. In an exampleembodiment, substantially flat top portion 51 has a substantiallycircular shape so that its surface area SA is well approximated by therelationship SA=π[D_(T)/2]². The total contact area SA_(T) presented bya set of n glass-bump spacers 50 is approximated by SA_(T)=πn[D_(T)/2]².

The size, shape and height of glass-bump spacers 50 can be moreaccurately controlled by using more complicated growth-limitingconfigurations or by altering the cross-sectional shape of focused laserbeam 112F. An advantage of controlling bump height H is that itmitigates the variability in bump heights due to glass non-uniformityand minor laser instability. These two factors, if unchecked, can resultin a bump-to-bump height variation in glass-bump spacers 50 of up to+/−5 μm. Another advantage of substantially flat-top glass-bump spacers50 is the reduction (including the minimization) of mechanical stressesat the contact point between tip portions 51 and glass 20F.

Apparatus 100 enables glass-bump spacers 50 to have a hemisphericalshape largely because the swelling of the glass that causes bumpformation is controlled by the surface tension of the molten glass. Thiseffect is exploited by using a focused laser beam 112F having acircularly symmetric cross-section. A rounded profile for glass-bumpspacers 50 is advantageous in that it provides minimal total contactarea S_(AT) between the glass-bump spacers and the adjacent glass pane,thereby reducing the heat conductivity between the two glass panes. Itis important to reduce (and preferably minimize) this heat transfermechanism in VIG windows 10 because thermal insulation diminishes withincreased total contact area S_(AT). in the other hand, a very smallcontact area SA per glass-bump spacer 50 may lead to local stressconcentration and can potentially damage the adjacent glass pane 20and/or glass-bump spacers 50. As discussed above in connection with FIG.11, glass-bump spacer 50 can have a substantially flat top portion 51whose size (i.e., diameter D_(T) and thus contact area SA) can becontrolled.

In an example embodiment of VIG window 10, the total contact area SA_(T)is selected to increase and preferably optimize the thermal insulation.It is estimated that for glass-bump spacers 50 having a base diameterD_(B) in the range from about 300 μm to about 700 μm, the substantiallyflat top portion 51 preferably has a “top” diameter D_(T)≦100 μm, morepreferably D_(T)≦75 μm, and even more preferably D_(T)≦50 μm.

To assess the visibility of laser-grown glass-bump spacers 50 in VIGwindow 10 versus that of discrete spacers used in conventional VIGwindows, several photos were taken at different tilt angles relative tothe surface normal of the VIG window. While glass-bump spacers 50 werevisible when viewed at glazing incident angles, they became practicallyinvisible at the more usual near-incident viewing angles. The photos ofVIG window 10 were then compared to photos taken under virtuallyidentical conditions for a commercial window pane having discreteceramic spacers. The discrete ceramic spacers were much more visible,particularly at the usual, near-incident viewing angles.

As shown in FIG. 4A, in an example embodiment, glass-bump spacers 50 areformed in both sides 22M and 24M of middle glass pane 20M to formtriple-pane VIG window 10 shown therein. Double-side glass-bump spacers50 are formed in one example embodiment by altering the irradiationconditions as compared with forming single-side bumps. By way ofexample, in one approach glass-bump spacers 50 are formed in one side22M of glass pane 20M, and then the glass pane is turned over and moreglass-bumps are formed in the other side 24M. In this embodiment, it maybe necessary to slightly displace the two sets of glass-bump spacers 50formed in the respective sides of middle glass pane 20M to avoidirradiating the previously formed glass-bump spacers. The amount of thisdisplacement is, for example, equal to or up to about twice the basediameter D_(B), which is typically in the order of 200 μm to 700 μm andis thus quite small when compared to the size of a typical VIG window10.

It is anticipated that the use of integrally formed glass-bump spacers50 for VIG windows 10 will be more cost effective than disposing andfixing discrete (i.e., non-integral) spacers to a glass pane. This islargely because the present invention obviates the need for equipmentand processes for placing discrete spacers in precise positions andkeeping them in place while assembling the VIG window. Because of thesmaller and controllable contact area SA between the tip portion 51 ofglass-bump 50 and adjacent glass pane 20, heat transfer through VIGwindow 10 via thermal conduction is reduced (and preferably minimized)relative to the use of discrete spacers. Cost advantages become evenmore evident in the case of manufacturing a triple-pane VIG window,where handling and placement of the discrete spacers is quitechallenging.

Example embodiments of VIG window 10 employ glass panes 20 havingdifferent material compositions. For example, one glass pane 20 (e.g.,back glass pane 20B in FIG. 2) is formed from a first glass type andanother glass pane (e.g., front glass pane 20F) is formed from a secondglass type. For example, the first glass type is soda-lime window glasswhile the second glass type is a sodium aluminosilicate glass (e.g.,1317, 2317, and others), or vice versa.

Furthermore, in an example embodiment of VIG window 10, one glass pane20 is thicker (e.g., 3 mm to 6 mm) to provide structural strength, whilethe other glass pane has a higher swelling capability and is thinner(e.g., 1 mm to 2 mm) to minimize the total thickness and weight of VIGwindow 10.

Glass-bump formation experiments conducted in sodium aluminosilicateglass 1317 (“1317 glass”) revealed a high degree of swelling capability,with bump heights H of 155 μm formed in a sample having a thicknessT_(G)=1.3 mm. It is noted here that soda-lime window glass and 1317glass have similar coefficients of thermal expansion (CTEs) of about 9ppm/C.

In experiments conducted in “ultra-white” window glass panes 20 thathave a very low iron content (and thus do not have a greenish tint),glass-bump spacers 50 with bump heights H of about 212 μm were formedusing the above methods. Thus, in an example embodiment, glass-bumpspacers 50 formed in low-iron content glasses have a bump height H inthe range from 75 μm to 225 μm, more preferably in the range from 100 μmto 225 μm, and even more preferably in the range from 150 μm to 225 μm.

FIG. 12 is a schematic side view of an example glass pane 20 that has aninfrared-reflective coating 210 in back surface 24. Such glass panes areuseful in VIG windows because they further reduce the amount oftransmitted heat.

FIG. 13 is a close-up cross-sectional view similar to that of FIG. 12,but for the IR-reflective glass pane 20 of FIG. 12, showing a glass-bumpspacer 50 formed thereon. Since coating 210 has a much lower meltingpoint than glass pane 20, it melts away from the vicinity of glass-bumpspacer 50, leaving it uncoated. Any remnants of coating 210 are easilyremoved by cleaning back surface 24 using standard glass cleaningtechniques.

VIG Window Formation

An aspect of the invention is directed to forming a VIG window, such asVIG window 10, using the methods of forming glass-bump spacers 50 asdescribed above. Thus, with reference again to FIG. 1 and FIG. 2, anexample method of forming a VIG window 10 includes forming, in a first(back) glass pane 20B comprising a first glass material, a plurality ofglass-bump spacers 50 consisting of the first glass material from thefirst body portion 23. The method then includes bringing a second(front) glass pane 20F of a second glass material in contact with thefirst plurality of glass-bump spacers 50 so that the first and secondglass panes are spaced apart by first distance D_(G) between respectivesurfaces 24F and 24B, as shown in FIG. 2. The method then includessealing at least respective portions of the first and second edges 28Fand 28B with edge seal 30 to define interior region 40 between front andback glass panes 20F and 20B. Interior region 40 is then at leastpartially evacuated to form a vacuum pressure therein of less than oneatmosphere. In a particular example embodiment, the first and secondglass materials are the same.

The method of forming a three-pane VIG window 10 is similar to theformation of the two-pane VIG window and is now discussed with referenceto FIG. 4A and FIG. 4B. With reference to FIG. 4A, in an exampleembodiment the formation of three-pane VIG window 10 involves formingtwo sets of glass-bump spacers in a middle (“first”) glass pane 20M thatresides between front (second) and back (third) glass panes 20F and 20B.Middle glass pane 20M thus has first and second pluralities (sets) ofglass-bump spacers 50 in respective surfaces 22M and 24M. Middle glasspane 20M also has an outer edge 28M and is made up of a first glassmaterial.

The method includes bringing the front and back glass panes 20F and 20B(made up of a second and third glass materials, respectively) inrespective contact with the first and second plurality of glass-bumpspacers 50 so that front middle and back glass panes 20F and 20M arespaced apart by a distance D_(GA) between surfaces 24F and 22M, and sothat middle and back glass panes 20M and 20B are spaced apart by adistances D_(GB) between surfaces 24M and 24B. The method then includessealing at least respective portions of the front, middle and back edges28F, 28M and 28B of the three glass panes with one or more edge seals 30(one edge seal 30 is shown in FIG. 4A). This serves to define first andsecond interior regions 40A and 40B between the front and middle glasspanes 20F and 20M and the middle and back glass panes 20M and 20B,respectively. Interior regions 40A and 40B are then at least partiallyevacuated to form respective vacuum pressures therein of less than oneatmosphere. In a particular example embodiment, the first, second andthird glass materials are all the same.

In an alternate embodiment shown in FIG. 4B, rather than forming thesecond set of glass-bump spacers 50 in middle glass pane 20M, they areformed in the inner surface 24B of back glass pane 20B. Also, as shownin FIG. 4B, the method of forming triple-pane VIG window 10 alternatelyincludes using one edge seal 30 to seal at least respective portions ofedges 28F and 28M to form the vacuum seal for first interior regions40A, and another edge seal to seal at least respective portions of edges28M and 20B to form the vacuum seal for second interior region 40B.

In the foregoing description, it will be readily appreciated by thoseskilled in the art, that modifications may be made to the inventionwithout departing from the concepts as disclosed herein, suchmodifications are to be considered as included in the following claims,unless these claims by their language expressly state otherwise.

What is claimed is:
 1. A method of forming a vacuum-insulated glass(VIG) window, comprising: in a first glass pane having a first bodyportion with a first surface and a first edge and comprising a firstglass material, integrally forming in the first surface a firstplurality of glass-bump spacers consisting of the first glass materialfrom the first body portion; bringing a second glass pane having asecond surface and a second edge and comprising a second glass materialin contact with the first plurality of glass-bump spacers so that thefirst and second glass panes are spaced apart by a first distancebetween the first and second surfaces; sealing the first and secondedges to define an interior region between the first and second glasspanes; and forming a vacuum pressure of less than one atmosphere in theinterior region wherein integrally forming the first plurality ofglass-bump spacers further comprises: a) irradiating the first glasspane at a location with a focused laser beam so that glass bump spacersare formed in the first glass pane, and terminating the irradiating tofix the glass-bump spacer; and b) repeating act a) a plurality of timesfor different locations to form the first plurality of glass-bumpspacers.
 2. The method of claim 1, wherein a feedback sub-system is usedto control a bump height of each respective glass-bump spacer.
 3. Themethod of claim 2, wherein the feedback sub-system measures atransmission intensity of the focused laser beam through the first glasspane and terminates the irradiating when a predetermined transmissionintensity value is measured.
 4. The method of claim 2, where thefeedback sub-system measures a temperature of each respective glass-bumpspacer and terminates the irradiating when a predetermined temperaturevalue is measured.
 5. The method of claim 2, where the feedbacksub-system measures a fluorescence intensity emanating from eachrespective glass-bump spacer and terminates the irradiating when apredetermined fluorescence intensity is measured.
 6. The method of claim2, where the feedback sub-system measures a bump height of eachrespective glass-bump spacer and terminates the irradiating when apredetermined bump height is measured.
 7. The method of claim 1,including providing the focused laser beam with one of an ultravioletwavelength and a mid-infrared wavelength.
 8. The method of claim 1,further comprising: positioning a growth-limiting surface adjacent thefirst glass pane surface and growing the glass-bump spacers into thegrowth-limiting surface, thereby providing the first plurality ofglass-bump spacers with substantially flat top portions.
 9. The methodof claim 1, further comprising: providing the focused laser beam withlight pulses having a temporal pulse width τ_(P) defined by 20ns≦τ_(P)≦80 ns, and a repetition rate R defined by 50 kHz≦R≦200 kHz. 10.The method of claim 1, wherein the first and second glass materials arethe same.
 11. The method of claim 1, further comprising: forming theglass-bump spacers to have a bump height H defined by 75 μm≦H≦225 μm.12. The method of claim 1, wherein at least one of the first and secondglass materials comprises soda lime glass.
 13. A method of forming avacuum-insulated glass (VIG) window, comprising: providing a first glasspane having a first body portion with a first surface and a first edgeand comprising a first glass material; irradiating the first glass paneat a plurality of locations with a laser beam to create a firstplurality of glass-bump spacers integrally formed in the glass pane;bringing a second glass pane having a second surface and a second edgeand comprising a second glass material in contact with the firstplurality of glass-bump spacers so that the first and second glass panesare spaced apart by a first distance between the first and secondsurfaces; sealing the first and second edges to define an interiorregion between the first and second glass panes; and forming a vacuumpressure of less than one atmosphere in the interior region.
 14. Themethod of claim 12 further comprising the step of terminating theirradiating to fix the height of ones of the first plurality ofglass-bump spacers.
 15. The method of claim 14, wherein the step ofterminating includes measuring a transmission intensity of the laserbeam and terminating the irradiating when a predetermined transmissionintensity value is measured.
 16. The method of claim 14, wherein thestep of terminating includes measuring a temperature of each respectiveglass-bump spacer and terminating the irradiating when a predeterminedtemperature value is measured.
 17. The method of claim 14, wherein thestep of terminating includes measuring a fluorescence intensityemanating from each respective glass-bump spacer and terminating theirradiating when a predetermined fluorescence intensity is measured. 18.The method of claim 14, wherein the step of terminating includesmeasuring a bump height of each respective glass-bump spacer andterminating the irradiating when a predetermined bump height ismeasured.
 19. The method of claim 14 wherein the step of terminatingincludes positioning a growth-limiting surface adjacent the first glasspane surface and growing the glass-bump spacers into the growth-limitingsurface.